The disclosure of Japanese Patent Application No. 2001-345639 filed on Nov. 12, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention generally relates to an air bag system installed in a vehicle, and more particularly to an air bag system which protects a vehicle occupant or occupants by inflating an air bag, which is stored in a folded state in a certain portion of the vehicle, using the gas supplied from an inflator.
2. Description of Related Art
In a known air bag system of the above type, for example, an air bag is stored along a roof side rail and is inflated by the gas supplied from an inflator into the shape of a curtain along a side wall of a passenger compartment of the vehicle, in order to protect a vehicle occupant or occupants from head injury. In another example of such an air bag system, an air bag stored in an instrument panel is inflated by the gas supplied from an inflator toward the inside of a passenger compartment of the vehicle, in order to protect a vehicle occupant or occupants from head and chest injuries.
In an air bag system disclosed in, for example, Japanese Laid-Open Patent Publication No. 11-321536, an inner tube is disposed along a gas passage (a gas inlet portion) of an air bag in order to reduce the degree of so-called xe2x80x9cbag damagexe2x80x9d, a damage caused to the air bag by the gas supplied from an inflator. In the air bag systems disclosed in Japanese Laid-Open Patent Publications No. 11-301394 and No. 2000-127886, a tubular member (a protection member) is disposed along a gas passage of an air bag in order to reduce the degree of bag damage due to the gas supplied from an inflator.
According to the above air bag systems, however, the inner tube or the tubular member (protection member), disposed along the gas passage of the air bag for reducing the degree of bag damage, obstructs the air bag to be folded, thus reducing the ease of storing the air bag in the vehicle and causing an increase in the cost of the air bag.
In general, air bag systems are constructed so as to satisfy several requirements related to the deployment performance of the air bag, such as a requirement for making the time from the beginning of the deployment of the air bag until its completion equal to or shorter than a predetermined time, a requirement for maintaining the initial internal pressure of the air bag equal to or higher than a predetermined high pressure from the beginning of the deployment of the air bag until its completion, and a requirement for maintaining the internal pressure of the air bag equal to or higher than a predetermined low pressure for a predetermined time from the elapse of a predetermined initial time since the completion of the deployment of the air bag.
When it is necessary to reduce the time required for completing the deployment of the air bag or increase the initial pressure of the air bag for satisfying the requirements as described above, the gas supply power of the inflator is generally increased. When the gas supply power of the inflator is increased, however, it increases the degree of bag damage, thus making it difficult or impossible to maintain the internal pressure of the air bag for a long time. In such a case, therefore, it is necessary to reduce the degree of bag damage by applying a sufficient amount of a coating material for guaranteeing airtightness to the air bag in order to increase its airtightness or by forming the air bag from the material having an increased airtightness, before increasing the gas supply power of the inflator. In this way, an improvement of the deployment performance of the air bag and a reduction of the cost of the air bag can not be achieved at the same time. This problem, however, is sure to be solved if it is possible to reduce the degree of bag damage at low cost.
In view of the above problem, the invention provides an air bag system which protects a vehicle occupant or occupants by inflating an air bag, stored in a folded state in a certain portion of a vehicle, using a gas supplied from an inflator, in which air bag system a preliminary inflatable portion is formed in a gas supply port of the air bag and a gas distribution portion of a diffuser serving to guide gas from the inflator into the air bag is arranged within the preliminary inflatable portion.
In the air bag system constructed as described above, gas is supplied to the preliminary inflatable portion formed in the gas supply port of the air bag from the inflator through the gas distribution portion of the diffuser, and the gas is then supplied to other portions (other inflatable portions) of the air bag from the preliminary inflatable portion while being dispersed in three-dimensional directions. Thus, the gas is temporarily stored in the preliminary inflatable portion in the early stage of the deployment of the air bag 11. At this time, therefore, the gas pressure in the preliminary inflatable portion becomes temporarily high while the gas pressures in the other portions (the portions of the air bag to which the dispersed gas is supplied) of the air bag 11 do not.
According to the above-described air bag system, therefore, it is possible to reduce the degree of xe2x80x9cbag damagexe2x80x9d, a damage caused to the air bag by the gas supplied from the inflator, and enhance the airtightness of the air bag at low cost by only increasing the thickness of a coat for guaranteeing airtightness to be formed on the surface of the preliminary inflatable portion. Also, gas is dispersed in three-dimensional directions when it is supplied from the preliminary inflatable portion to the other portions of the air bag, therefore the gas supply can be efficiently performed to reduce the time required for completing the deployment of the air bag. As a result, an improvement of the deployment performance of the air bag and a reduction of the cost of the air bag can be achieved at the same time.